a) Field of Invention
The present invention relates to a living body stimulating apparatus, such as a low-frequency electro-therapeutic device, for stimulating a living body by attaching a conductor element with a built-in electrode to a living body to thereby allow electric current to flow through the electrode into the living body.
b) Prior Art
In general, such type of living body stimulating apparatus is aimed at the treatment of nerve function in a diseased part, by allowing a low frequency pulse current to flow in the diseased part, said low frequency pulse current being output from a transmitter to an electrode. In Japanese Patent Un-Examined Publication No.1-146562, for example, is disclosed a living body stimulating apparatus which enables the control of the speed and intensity of stimulation, by switching stimulation signals output from an output circuit to a living body (or human body) to either one of DC intermittent pulses for periodically outputting positive pulses, AC intermittent pulses for periodically outputting rectangular wave pulse groups consisting of positive pulses and negative pulses, and Alternate intermittent pulses for periodically and alternately outputting positive pulses and negative pulses, and/or by varying the period or amplitude of the respective intermittent pulses.
In the meantime, a human body is generally hard to pass an electric direct current therethrough, which has a resistance of about 100 kxcexa9 that varies depending upon voltage, whilst an alternate electric current of high-frequency is relatively easy to flow through a human body. For example, a human body indicates a resistance of about 1 kxcexa9 under an AC voltage of 1 kHz, said resistance being reduced by half if a frequency doubles. In other words, a human body has a sort of a capacitance like that of a capacitor, so that it has a tendency to decrease in-vivo resistance as a frequency increases. On the other hand, from a standpoint of a feel of stimulus against a human body, low frequencies which are close to direct current, and rectangular waves involving many D.C. components (or straight portions) get more stimulative, and thus if a frequency is the same, sinusoidal waves will impart more moderate or softer stimuli than rectangular waves.
FIG. 5 illustrates an example of a conventional living body stimulating apparatus for imparting stimulation signals in the form of sine waves to a human body. In the drawing, numeral 101 designates CPU (central processing unit) as a control means, which outputs digital data signals which are then converted into analogue data signals by D/A circuit 102. Then, the analogue data signals are amplified by a amplifier circuit 103, to thereby make the sine-wavelike stimulation signals come out between conductive elements or output electrodes 105 across a transformer 104. In that case, the amplitude of the sine wave is capable of being freely increased or decreased by operating an output variable volume lOG connected to a front side of the amplifier 103.
Although such sinusoidal wave does impart a soft feel of stimulation and thus it is desirable to a human body, yet it includes a single frequency component only, thus leading to a great disadvantage in obtaining extensive therapeutic effects. Further, in an output circuit for use in such apparatus, socalled analogue circuits such as the D/A circuit 102 and the amplifier circuit 103 have to be used for obtaining a substantially sinusoidal waveform, and thus the number of components inevitably increases and the structure of circuits becomes more complex, thus leading to bad power efficiency. In other words, conventional circuits for output of sinusoidal waves would require dozens of components such as transistors, resistors and capacitors.
To eliminate the above problems, it is a main object of the invention to provide a living body stimulating apparatus which realizes extensive therapeutic effects with soft stimuli being imparted to a living body.
To attain the above objects, there is proposed a living body stimulating apparatus for imparting stimuli to a living body by attaching electrodes to the living body so as to pass electric current through the living body via the electrodes, which comprises: a stimulus generator for subjecting recurringly output rectangular wave pulses to pulse width modulation, and then outputting the recurrence of rectangular wave pulse groups serving as stimulation signals to the electrodes, each rectangular wave pulse group including a plurality of frequency components higher than said rectangular wave pulse.
It should be noted that the present invention has been made, focusing on the fact that a living body has a property similar to that of a capacitor. With the above-mentioned structure, when the stimulus generating means is allowed to modulate the width of rectangular pulses which are output at a predetermined recurrence frequency, then a living body is supplied with the recurrence of pulse groups each of which includes a plurality of signal components whose frequencies are higher than that of the rectangular wave pulse, said recurrence of pulse groups serving as stimulating signals supplied from the output electrodes. At that time of moment, as a living body has such a capacitor-like property, the higher frequency the signal component has, the lower impedance it will result in, so that the waveform of the rectangular pulse group is distorted as a whole, thereby generating softer feel of stimulation than ordinary rectangular wave pulses that have the same current and frequency. In addition, as each rectangular wave pulse group includes signal components of higher frequency than that of the original rectangular wave pulse, extensive therapeutic effects can be expected from such signal component of the higher frequency.